Electronic watch movement comprising time display means having indicator hands

ABSTRACT

The movement comprises a bottom-plate (1), a gear-train bridge (2), a center gear (14), an hour wheel (24) and a cell (25). The center gear (14) has a shaft (15) and a wheel (19) frictionally mounted on the shaft (15). Within the thickness of the movement, the frictionally mounted wheel (19) is adjacent the cell (25) to one side and the hours wheel (24) to the other side. The movement is so designed that the center gear (14) and the hours wheel (24) may be fitted into place at the very end of the assembly process.

BACKGROUND OF THE INVENTION

This invention relates to electronic watch movements comprising analogtime display means and more particularly those having only an hours handand a minutes hand.

Such movements are generally intended to watches of small size, e.g.ladies' watches. In such watches, it is desirable for the cell to be asclose as possible to the center of the watch. To this end, the movementdescribed in swiss patent specification 615068 comprises a bottom-plateon which is provided a central peg on the dial side. On this peg arepivotally mounted the cannon-pinion and the hours wheel, whichrespectively mesh with the minutes wheel and the minutes pinion. Thekinematic connection with the rotor is thus solely provided by theminutes gear. This arrangement enables the center of the movement to becleared and hence a cell of large diameter to be used, but gives rise toa major drawback: since the cannon-pinion is at the end of the kinematicchain provided by the gear-train and thus, necessarily, has only fewteeth, the backlash is quite substantial. As a result, the position ofthe minutes hand becomes somewhat inaccurate, unless a brake is appliedon the cannon-pinion. But such a brake would increase the energyconsumption of the watch and a larger cell would then be needed toachieve a corresponding autonomy.

In the specification of Japanese patent application 57-161578, amovement is described having a bottom-plate, a gear-train bridge, arotor, an intermediate gear and an hours wheel. The center gear has ashaft that is pivotally mounted between the bridge and the bottom-plateand on which a wheel web is frictionally mounted. The shaft takes up theentire height of the movement while the wheel web is housed in a spacebetween the bottom-plate and the cell. This arrangement lends itself tothe design of a watch in which the cell extends close to the centerwithout giving rise to a backlash problem with the center gear. But thisresult is achieved at the expense of the thickness of the cell.

SUMMARY OF THE INVENTION

An object of the invention is to remedy these defects with aconstructional arrangement that still makes it feasible for a cell toextend as close as possible to the center of the movement, and with acell thickness almost equal to the height of the movement.

According to the invention, the invention provides an electronic watchmovement comprising a bottom-plate having a central opening, a cell,time display means having indicator hands, a motor and a gear-trainconnecting the motor to the indicator hands, said gear-train includingan intermediate gear, a center gear having a shaft and having a wheeland a pinion solid with said shaft, a minutes gear and an hours wheel,having a pipe, rotatably mounted on said shaft directly over the wheelof said center gear, the wheel of said center gear meshing with teeth onsaid intermediate gear and extending over said cell, and the centralopening in said bottom-plate having a diameter larger than that of thepinion of said center gear.

SHORT DESCRIPTION OF THE DRAWINGS

In the accompanying diagrammatic drawings, in which the same referencenumbers are used to designate corresponding parts:

FIGS. 1 and 3 are cross-sections through a part of two movementsaccording to the invention; and

FIGS. 2 and 4 are again cross-sections through a part of the samemovements but along a different line.

DETAILED DESCRIPTION

The movement shown in FIGS. 1 and 2 comprises a frame made up of abottom-plate 1 and of a gear-train bridge 2. Between these two frameelements is mounted a motor, not shown, whose rotor has a pinion thatmeshes with a first intermediate gear 3, in particular with the wheel 4thereof. The pinion 5 of gear 3 meshes with the wheel 6 of a secondintermediate gear 7 whose pinion 8 consists of a toothed dish-like discsolid with shaft 9 of gear 7. Shaft 9 has two pivots 10 each engaged ina jewel 11. One of these jewels is set into a hole provided inbottom-plate 1 at the center of a boss 12 that projects inwardly of themovement. Bottom-plate 1 is also formed with a central recess 1a whosebottom 13 is burst to enable toothed disc 8 to mesh with a center gear14 which will now be described. Center gear 14 has a shaft 15 integralwith its pinion 16 and a pivot 17. Pivot 17 is supported by a bearing 18provided by a jewel that is set in a hole formed in bridge 2. Centergear 14 further comprises a wheel 19 having a toothed web 19a, a boss19b, a collar 20 adjacent web 19a and, between web 19a and collar 20, acircumferential groove 21 coaxial with gear 14. Wheel 19 has the samenumber of teeth as toothed disc 8. These two elements mesh when thecenter gear is fitted into place. Collar 20 has an outer diameter whichis slightly larger than that of pinion 16. Collar 20 rotatably engagesin a hole 22 formed in the bottom 13 of central recess 1a inbottom-plate 1. Consequently, hole 22 defines a central opening inbotom-plate 1 which is larger than center pinion 16.

Wheel 19 is frictionally mounted on shaft 15. These two parts are thussolid with one another. The pivotal motion of center gear 14 is ensuredfirstly by collar 20, engaged in hole 22, and secondly by pivot 17,engaged in jewel 18. In the described form of embodiment, an elasticlocking element 23 that is secured by a screw to the bottom 13 of recess1a in bottom-plate 1 blocks center gear 14 axially but, as will beapparent later, this arrangement is not essential.

As in a normal movement, the time display means include an hours wheel24, having a pipe portion, which is rotatably mounted on shaft 15 ofcenter gear 14 over wheel 19 and ears on boss 19b. The pipe portion ofwheel 24 is intended to carry an hours hand, not shown, while the endportion of shaft 15 of center gear 14 is intended to carry a minuteshand, not shown either.

Cell 25 for energizing the movement is put in place from the back of themovement into a hollow or a hole in gear-train bridge 2. It bearsagainst a beveled surface 26 on bottom 13 of central recess 1a inbottom-plate 1. Between the top surface of cell 25 and the portion ofbottom-plate 1 that extends over cell 25 sufficient space is provided toaccommodate an electrical connection tongue, not shown. Wheel 19 alsoextends into this space, while the web of hours wheel 24 extends in theplane of the upper portion of bottom-plate 1. Radically, cell 25 extendsto a distance from the center of the movement that is slightly largerthan the radius of pinion 16.

Wheels 19 and 24 are also visible in FIG. 2. Pinion 16 meshes with thewheel 27 of a minutes gear 28 having a pinion 29 that is driven into acollar 30. Collar 30 has a diameter slightly larger than that of pinion29 and is rotatably mounted in a hole 31 in bottom-plate 1. Minutespinion 29 meshes with hours wheel 24 whilst minutes wheel 27, whichmeshes with center pinion 16, may also be driven manually upondisplacement of a sliding pinion 32 along the square of a control stem33. The latter extends radially in the movement. A lever 34 and apull-out piece, not shown, move sliding pinion 32 in the usual way whenstem 33 is pulled outwardly into its time-setting position. This designfor the movement thus involves no setting wheel in the time-settingmechanism.

The movement shown in FIGS. 3 and 4 mainly differs from the first inthat center gear 14 is rotatably mounted on a peg 35 secured ingear-train bridge 2. More specifically, peg 35 has a seat 36 that isforce-fitted into a hole 37 in bridge 2, and a pivot 38 that rotatablyengages into a hole 39 in shaft 15 to enable the latter to pivot. Pivot38 and shaft 15 each have an annular rib, 40 and 41 respectively, whichribs are adapted to interengage to define an axial snap arrangement foraxially positioning center gear 14. Further, center wheel 19 does nothere have a collar nor a groove, center gear 14 being guided andpositioned by peg 35 alone. In this embodiment also, bottom-plate 1instead of having a recess in its center is formed with a plain centralopening 1b through which the entire center gear 14 along with centerwheel 19 and hours wheel 24 may be fitted into place.

In both of the above described embodiments, the minutes hand is borne bya shaft driven by a wheel of large diameter, i.e. center wheel 19,thereby considerably reducing backlash. Nonetheless, the space availableheightwise within the movement for receiving the cell exceeds 60% andmay be as much as 90% of the thickness of the movement, despite the factthat the cell comes to within the immediate vicinity of the movement'scenter.

This arrangement also has an interesting complementary advantage, as itenables center gear 14 and hours wheel 24 to be put into place after themovement has otherwise been fully assembled. In the first embodiment, itsuffices to engage pivot 17 into the hole of jewel 18 and to causecollar 20 to penetrate hole 22 in bottom-plate 1. In the secondembodiment, center gear 14 is simply engaged over pivot 38. this enablesmovements to be stocked without a center gear and without an hours wheeland enables the selection, at the time of delivery, of a center gear andof an hours wheel in dependence on the height of the hands assembly. Itmight even be possible to mount the minutes hand and the hours hand onthe center gear and on the hours wheel respectively, with the dial beingsandwiched in between, the resulting module being then fitted to thewatch movement.

What is claimed is:
 1. An electronic watch movement comprising abottom-plate having a central opening, a cell, time display means havingindicator hands, a motor and a gear-train connecting the motor to theindicator hands, said gear-train including an intermediate gear, acenter gear having a shaft and having a wheel and a pinion solid withsaid shaft, a minutes gear and an hours wheel, having a pipe, rotatablymounted on said shaft directly over the wheel of said center gear, thewheel of said center gear meshing with teeth on said intermediate gearand extending over said cell, and the central opening in saidbottom-plate having a diameter larger than that of the pinion of saidcenter gear.
 2. A movement according to claim 1, wherein the wheel ofsaid center gear and the hours wheel are accommodated in anoutwardly-opening recess in said bottom-plate.
 3. A movement accordingto claim 2, wherein said center gear has, between its wheel and itspinion, a collar having a diameter larger than that of said pinion andwhich guides said center gear during rotation in the central openingprovided in the bottom of said bottom-plate recess.
 4. A movementaccording to claim 3, wherein said center gear further comprises a pivotrotatably mounted in a bearing solid with a gear-train bridge.
 5. Amovement according to claim 1, wherein the wheel of said center gear andthe pinion of said intermediate gear have the same number of teeth.
 6. Amovement according to claim 1, wherein said center gear is axially heldin place by a locking element that engages in a circumferential grooveco-axial with said center gear and located in the latter between itswheel and its pinion.
 7. A movement according to claim 1, furthercomprising a gear-train bridge having a peg extending towards saidbottom-plate and engaged in an axial hole comprised by said center gearto rotatably mount said center gear on said peg.
 8. A movement accordingto claim 7, wherein said peg and the wall of said hole are each formedwith an annular rib, said ribs being interengageable to define an axialsnap for axially positioning said center gear on said peg.
 9. A movementaccording to claim 2, wherein said center gear is axially held in placeby a locking element that engages in a circumferential groove co-axialwith said center gear and located in the latter between its wheel andits pinion.
 10. A movement according to claim 3, wherein said centergear is axially held in place by a locking element that engages in acircumferential groove co-axial with said center gear and located in thelatter between its wheel and its pinion.
 11. A movement according toclaim 4, wherein said center gear is axially held in place by a lockingelement that engages in a circumferential groove co-axial with saidcenter gear and located in the latter between its wheel and its pinion.12. A movement according to claim 5, wherein said center gear is axiallyheld in place by a locking element that engages in a circumferentialgroove co-axial with said center gear and located in the latter betweenits wheel and its pinion.
 13. A gear for use in a timepiece having ashaft, a pivot at one end of the shaft, a pinion integral with saidshaft and a separate wheel, integral with a journal-forming collar andsolid with said shaft, wherein said collar has a diameter greater thanthat of said pinion and is located between said wheel and said pinionfor guiding said gear during rotation thereof in an opening provided ina plate of said timepiece.